APF (All Plastic Fiber) has high transmission loss and it is a disadvantage in the optical communication. If it has been used in an optical network with distributed signals, like star type, optical signals are reduced at the star coupler due to scattering loss and insertion loss caused by ray distribution. Therefore, we can use a passive star coupler only in a small area.
One possible solution is light amplification at the optical star coupler using a feed back method. The feed back amplifier is composed of a pair of E/O (Erectrical/Optical), O/E (Optical/Electrical) converters using one channel in the passive star coupler. It has a performance that is able to increase the output level about 3dB at each output port. So, it enables communication between nodes with certainty. We named ACTIVE STAR COUPLER.